Roger Federer
After three years beset by injury you could've been forgiven for thinking the Swiss maestro's historic reign atop the tennis world was destined for the inevitable downward slope towards retirement.
We should've known he wasn't going to settle with a clichéd limp from the international stage.
Instead, the 36-year-old stormed to his most successful season, according to win percentage, since 2006.
Highlighted by grand slam triumphs in Australia and Wimbledon, the Fed Express returned to the peak of his powers in 2017 and is clearly some way yet from calling time on what is arguably already the greatest career the sport has ever seen.
Panthers vs Warriors – Round 10 NRL
It's a memory many begrudged Warriors fans have buried deep in the recesses of their minds, yet it's one which probably best encapsulates their 2017 NRL campaign.
Ahead 28-6 at halftime after running in five tries during an opening stanza blitz, you'd think you'd probably feel secure in the knowledge that you have two competition points in the bag, right?
Not if you're familiar with the special kind of struggle that comes with being a Warriors fan.
And so it played out, the Panthers running in 36 unanswered points in the second half to clinch an improbable 36-28 win and consign the Auckland-based club to their greatest/worst collapse ever.
Patriots vs Falcons - Superbowl
NFL fans could scarcely believe what they were seeing as Falcons quarterback Matt Ryan conducted his juggernaut offense to a 28-3 lead just minutes into the second half of Superbowl LI.
Leave it to Mr Captain America, Tom Brady, to orchestrate the biggest comeback in the history of American sports' showcase event.
A Julian Edelman wonder-reception sparked the run which ended with a diving James White touchdown in overtime to send Boston into a state of delirium.
It was a victory that tasted all the more sweet after a season of derision and controversy centred around the use of intentionally deflated balls the year prior.
Barcelona vs Paris St.Germain – Champions League
Later dubbed "The Miracle at Nou Camp", Barcelona's startling resurgence from a 5-1 deficit against Paris St-. Germain has all the trimmings of an all-time classic.
Needing a 6-1 win to advance to the Champion League quarter-finals after their heavy defeat in Paris, the Catalans seemed to be staring down the barrel of early elimination heading into the final stanza of the second leg.
A glimmer of hope shone through when they went up 3-0, until it was seemingly extinguished by a valuable Cavani away goal in the 62nd minute.
Step forth Brazilian star Neymar, who struck twice in the dying moments of regular time before local lad Sergio Roberto volleyed home in the 96th minute to set the Nou Camp alight and cap the greatest comeback in European football history.
Georges St-Pierre
The French-Canadian superstar had already forged his name in the pantheon of MMA before he decided to make a return to the Octagon after a four-year hiatus from competition.
"Rush" chose to vacate his welterweight title and step away from the sport in 2013 after a second-straight war with Johny Hendrick, citing both mental and physical fatigue.
And there would be no talk of a warm-up bout to shed the rust upon his return. Instead he'd step right back into the fire, moving up a weight class to take on Michael Bisping for the UFC middleweight belt in New York City.
Many believed the combination of the veteran Briton's size and St. Pierre's lengthy layoff would be too much for St.Pierre to handle.
Instead it was GSP who would start the much stronger fighter, looking active and using his trademark jab to good effect. Bisping fought back to take the second round then lifted a notch in the third, opening his opponent up with a sustained elbow offensive.
Blood smeared across his face, GSP finally managed to get to his feet and moments later delivered a sting left hook to send the champ to the canvas, swarming with elbows of his own before sinking in a rear-naked choke to end the contest.
"I don't have words in my mouth right now," St-Pierre said in his post-fight interview.
"It's a dream come true. He hurt me very hard. I got stunned and tried to hide it. I wouldn't like to do that fight again."
Now one of just four two-division champions in UFC history, you could forgive him if he called it a day after such a fairytale result.
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